Featured Research

from universities, journals, and other organizations

Scientists unravel mechanisms in chronic itching

Date:

October 15, 2013

Source:

Washington University in St. Louis

Summary:

New research shows that chronic itching, which can occur in many medical conditions, is different from the urge to scratch a mosquito bite. Chronic itching appears to incorporate more than just the nerve cells that normally transmit itch signals. In chronic itching, neurons that send itch signals also co-opt pain neurons to intensify the itch sensation.

Anyone who has suffered through sleepless nights due to uncontrollable itching knows that not all itching is the same. New research at Washington University School of Medicine in St. Louis explains why.

Related Articles

Working in mice, the scientists have shown that chronic itching, which can occur in many medical conditions, from eczema and psoriasis to kidney failure and liver disease, is different from the fleeting urge to scratch a mosquito bite.

That's because chronic itching appears to incorporate more than just the nerve cells, or neurons, that normally transmit itch signals. The researchers found that in chronic itching, neurons that send itch signals also co-opt pain neurons to intensify the itch sensation.

The new discovery may lead to more effective treatments for chronic itching that target activity in neurons involved in both pain and itch. The research is reported online Oct. 15 in The Journal of Clinical Investigation and will appear in the November print issue.

"In normal itching, there's a fixed pathway that transmits the itch signal," said senior investigator Zhou-Feng Chen, PhD, who directs Washington University's Center for the Study of Itch. "But with chronic itching, many neurons can be turned into itch neurons, including those that typically transmit pain signals. That helps explain why chronic itching can be so excruciating."

Chen, a professor of anesthesiology, and his colleagues generated mice in which a protein called BRAF always is active and continually sends signals inside itch neurons. The BRAF gene and the protein it makes are involved in the body's pain response, but scientists didn't know whether the gene also played a role in itch.

"We thought the animals might be prone to feeling pain rather than itching," Chen explained. "To our great surprise, the mice scratched spontaneously. At first, we didn't know why they were scratching, but it turns out we developed a mouse model of chronic itch."

Further studies discovered that the BRAF protein could turn on many itch genes, and they showed similar changes of gene expression in mice with chronic itch induced by dry skin and in mice with allergic contact dermatitis, two of the skin conditions that frequently cause people to scratch incessantly.

The findings suggest that targeting proteins in the BRAF pathway may open new avenues for treating chronic itch, a condition in which few therapies are effective. One possibility includes using drugs that are prescribed to treat pain.

"Certain drugs are used to inhibit some of the same targets in patients with chronic pain, and those medications also may quiet down itch," Chen said.

In earlier studies, Chen identified gastrin-releasing peptide (GRP), a substance that carries itch signals to a gene called GRPR (gastrin-releasing peptide receptor) in the spinal cord. In the new study, GRP and GRPR activity was doubled in the genetically altered mice, which could account for some of the increase in the intensity of itching. But other genes that normally are activated by pain also were turned on in the itch pathway, further intensifying the itch sensation.

Surprisingly, however, the mice had a normal response to pain, indicating that the pain and itch pathways are very different.

Unlike scratching a mosquito bite, which usually is only a temporary sensation, chronic itch can persist much longer, according to Chen, also a professor of psychiatry and of developmental biology. His team found that the mice in this study not only scratched spontaneously but also had more severe responses when exposed to substances that normally would induce acute itching.

"In people, chronic itching can last for weeks, months or even years," Chen said. "These mice are helping us to understand the pathways that can be involved in transmitting itch signals and the many contributors to chronic itching. There are many pathways leading from BRAF, and all of these could be potential targets for anti-itch therapies."

Washington University in St. Louis. (2013, October 15). Scientists unravel mechanisms in chronic itching. ScienceDaily. Retrieved March 31, 2015 from www.sciencedaily.com/releases/2013/10/131015123338.htm

Mar. 31, 2015  Increasing state alcohol taxes could prevent thousands of deaths a year from car crashes, say researchers, who found alcohol-related motor vehicle crashes decreased after taxes on beer, wine and ... full story

Mar. 31, 2015  Alcoholism takes a toll on every aspect of a person's life, including skin problems. Now, a new research report helps explain why this happens and what might be done to address it. "The clinical ... full story

Mar. 31, 2015  A new population of 'memory' immune cells has been discovered by scientists, throwing light on what the body does when it sees a microbe for the second time. This insight, and others like it, will ... full story

Mar. 31, 2015  Coronary heart disease and stroke, two of the leading causes of death in the United States, are diseases associated with heightened platelet reactivity. A new study in humans suggests an underlying ... full story

Mar. 31, 2015  A new study had researchers seeking answers to why the therapeutic benefit afforded by SSRIs was so limited in children and teenagers. If researchers can uncover the biological mechanisms preventing ... full story

Mar. 31, 2015  A drug being developed to treat osteoporosis may also be useful for treating osteogenesis imperfecta or brittle bone disease, a rare but potentially debilitating bone disorder that that is present ... full story

Mar. 31, 2015  It is possible to quantify and classify the effects of different diseases on the activity of intestinal bacteria, new research demonstrates for the first time. Human intestinal flora, known as ... full story

Mar. 31, 2015  During prenatal development, the brains of most animals, including humans, develop specifically male or female characteristics. But scientists have known little about the details of how this ... full story

Mar. 31, 2015  A history of depression may put women at risk for developing diabetes during pregnancy, according to research. This study also pointed to how common depression is during pregnancy and the need for ... full story

Featured Videos

Solitair Device Aims to Takes Guesswork out of Sun Safety

Reuters - Innovations Video Online (Mar. 31, 2015)  The Solitair device aims to take the confusion out of how much sunlight we should expose our skin to. Small enough to be worn as a tie or hair clip, it monitors the user&apos;s sun exposure by taking into account their skin pigment, location and schedule. Matthew Stock reports.
Video provided by Reuters

Soda, Salt and Sugar: The Next Generation of Taxes

Washington Post (Mar. 30, 2015)  Denisa Livingston, a health advocate for the Dinι Community Advocacy Alliance, and the Post&apos;s Abby Phillip discuss efforts around the country to make unhealthy food choices hurt your wallet as much as your waistline.
Video provided by Washington Post

S. Leone in New Anti-Ebola Lockdown

AFP (Mar. 28, 2015)  Sierra Leone imposed a three-day nationwide lockdown Friday for the second time in six months in a bid to prevent a resurgence of the deadly Ebola virus. Duration: 01:17
Video provided by AFP

Related Stories

Oct. 30, 2014  Turns out your mom was right: scratching an itch only makes it worse. New research reveals that scratching causes the brain to release serotonin, which intensifies the itch sensation. Scientists ... full story

Sep. 24, 2014  Brain areas that respond to reward and pleasure are linked to the ability of the drug butorphanol to relieve itch, according to new research. The findings point to the involvement of the brain's ... full story

Oct. 13, 2011  Itching is one of the most prevalent side effects of powerful, pain-killing drugs like morphine, oxycodone and other opioids. Now in mice, researchers have shown they can control opioid-induced ... full story

Nov. 4, 2010  We all know how hard it is not to scratch when we have an itch. But how can an itch be alleviated? Researchers now present the surprising finding that the same nerve cells that are active when we ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.